Engine speed regulation



gorro Joarzou zut@ m doro Jourzou 422.200 D mman J. J. ROOT Filed May 6, 1947 ENGINE SPEED 'REGULATION h IL June 6, 1950 INVENTOR.

A TTOR NEY.

Patented June 6, 1950 UNITED STATES PATENT OFFICE 2 Claims.

This invention relates to electronic apparatus for adjusting the speed of an engine to any desired value and automatically maintaining the engine speed at the selected value.

The apparatus of my invention provides a light weight compact control unit which enables the speed of the engine to be set by a manual operation the same as it was prior to the installation of my apparatus. 'When applied to a helicopter engine its speed can be set by turning a potentiometer which may be mechanically connected to the throttle twist grip on the helicopter pitch control stick. The throttle is turned by a motor which is energized so as to have a large torque even at the lowest speeds of the motor. The electronic control unit forming a part of my invention varies the speed of the engine rapidly for large deviations from the desired speed and varies the speed of the engine more and more slowly as it approaches its proper value. Thus my apparatus achieves rapid, accurate and flexible control of the engine speed.

It is the object of my invention to provide electronic control apparatus which shall be light in weight, compact, simple to operate and shall rapidly, accurately and safely maintain an engine at the speed to which it is adjusted to operate.

The invention will be fully understood from the following description and drawings .in which:

Fig. l is a block diagram of the major components of my invention,

Fig. 2 is a diagram showing the eiiect of certain controls utilized in my apparatus, and

Fig. 3 shows a detailed circuit diagram of the control unit.

Fig. 4 is a circuit diagram of the power supply arrangement of the control unit.

Referring to Fig. l there is shown an engine l whose speed is to be adjusted and governed. The engine may be that of a helicopter although it will be evident that my control apparatus can be applied to any type of engine or apparatus the speed of which is to be governed. The tachometer generator 2 is connected to the engine and rotates therewith so that he speed of the engine is indicated exactly by the alternating voltage signal supplied by the tachometer. The tachometer is hence an intelligence unit Which transmits engine speed information to the electronic control unit 3. The output of the control unit energizes the motor 4 which changes the throttle adjustment of the helicopter engine l to correct for deviations from the desired engine speed. The speed of the engine may be adjusted by a speed control potentiometer P3. Both the potentiometer P3 and the control motor 4 may be mounted in the helicopter pitch control stick 5. The motor 4 may be connected to the throttle linkage '6 by a shaft extending through the pitch control stick 5. The throttle linkage 5 and the shaftconnected thereto are now used in mechanical throttle controls.

Referring now to Fig. 3 the tachometer 2 is shown connected across potentiometers Pl, P2, and P3. rlhe potentiometers P2 and P3 are connected to the tachometer 2 alternatively by the switch Si. The potentiometers P2 and. P3 serve similar functions but potentiometer P2 provides a local control for servicing and test operation while potentiometer P3 provides a remote operating control for the engine speed. The potentiometer Pl is connected to a high pass ilter Cl, C3, R2. The output of this high pass llter is rectied by a crystal or other type rectiiier Xi. .A voltage tapped off potentiometer P2 or P3 is applied through a, low pass filter Rl, C2 to a voltage doubling rectier. The voltage doubling rectier includes a condenser C4 and rectiers X2 and X3. The rectifiers Xi X2 and X3 are shunted by small protective condensers C5, Cl and Ct respectively. Because of the high pass nlter the voltage developed across the resistor R4 increases with frequency as indicated by the line 2l in Fig. 2. The voltage developed across the resistor Rt is a reference voltage and remains substantially constant with engine speed because as the tachometer speed increases its voltage increases so as to approximately compensate for the increas ing attenuation of the low pass iilter due to increasing frequency. The voltage across the re sistor R6 is represented by the lines 24, 25, or 2t, of Fig. 2. Lowering the tap on potentiometer Pi reduces the voltage across the resistor R4 so that it is represented by the lines 22 or 23 instead of the line 2l. Adjustment of the potentiometer Pl varies the range of engine speeds which may be obtained by adjustment ci the potentiometers P2 or P3. The potentiometer Pi is therefore used to set the range of engine speeds, and particularly the maximum speed desired, while potentiometer P3 is used to control the engine speed in operation.

When the engine is running at its proper speed the voltages across resistors R4 and R6 will be equal and opposite and in this case no voltage will be impressed across the resistors R5 and Rl. If the engine speed increases above the desired Value the upper end of resistor R5 becomes positive with respect to the lower end of resistor Rl. The control grid of the D. C. amplifier tube Vl then becomes positive with respect to ground and the control grid of tube V2 becomes negative. The plate current of tube Vl then increases while that of tube V2 decreases. The increased current through resistor R9 lowers the grid potential of tube V3, while the decreased current through resistor RIU raises the potential on the grid of tube V4. Conversely, a decrease of engine speed below the desired value will increase the potential on the grid of tube V3 and decrease the potential on the grid of tube V4.

Tubes V3 and V5 form a multivibrator producing substantially square wave pulses to accelerate the engine while V4 and V6 form a multivibrator producing similar pulses to decelerate the engine. When theI engine speed is greater than the desired value the negative potential on the grid of tube V3 blocks the acceleration multivibrator and the positive potential on the grid tends to start the deceleration multivibrator.. The voltages from the D. C. ampliiiers Vl and V2 required to start the multivibrators are determined by the setting of potentiometers Pit and P5. These potentiometers set the biases on the. cathodes of tubes V3 and Vfl.

When the voltage impressed on the grids of tubes V3 and V4 are only slightly greater than the starting voltage the condensers Cil and Cit are charged slowly by the plate currents of the tubes V3 and V4. For higher positive grid voltage on one of these tubes the plate current is greater and the condenser Cil or Cit is charged more rapidly. Potentiometers Pt and P'E control the rate of acceleration and deceleration, respectively, of the engine speed ier a given deviation thereof from its proper value. lt is the charging rate of these condensers through the potentiometers P6 and Pl which largely determines the repetition rate of the multivibrators. It can be seen that a large deviation from the desired engine speed will produce a higher repetition rate and correspondingly less pulse width than a small deviation. The effect oi making the repetition rate approximately proportional to the deviation is to increase the rapidity with which deviations are corrected, and to reduce the rate of correction as the engine speed approaches its proper value to thereby avoid over-run and hunting. Hunting is also decreased by setting the potenti--1 ometers P4 and P5 so as to permit certain minimum deviations from the selected engine speed without operating the multivibrators. Thus the potentiometers Pil and P set certain tolerances within which no corrections oi the engine speed are made. yThese tolerances can be made imma-f terially small so far as the performance of the airplane isconcerned, and yet be quite eii'ective in avoiding hunting.

The pulse output or" the multivibrators is fed through the coupling condensers C255 and Cid to the grids of tubes Vl and Vd. in the plate circuits of these tubes relays Li and L2 are connnected. In the unenergized position these relays ground the wires leading to the control motor d. Upon the occurrence of a pulsesay through the condenser C24, the relay Ll is energized and the moving contact thereof is connected to B+ conn necting one side of the motor d to B+ While leav ing the other side grounded and feeding a pulse to the motor to turn it in the desired direction. Operation of the relay L2 similarly feeds a pulse to the motor 4 in the opposite direction. In this manner each pulse received from the multivibrator feeds a current pulse of iixed amplitude to the motor 4. The rate of rotation of the motor will therefore be determined by the repetition rate of the multivibrators.

A iilter C2I, C22, RIS and R20 are connected across the movable contacts of the relays Ll and L2 to prevent sparking.

Another relay L3 is connected between resistors R|9 and R20 and directly to ground. Operation of relay L3 removes the short circuit across resistor R18 and condenser C23. The impedance of these last two elements is suiiicient to practically disconnect the motor. The resistors RIS and R20 may have such a value that the closing of either relay Ll or L2 for too long a time will be sufficient to operate relay L3 and interrupt the rotation of motor 4. Relay L3 thus affords protection against faulty operation, particularly I against excessive rotation of the motor 4 in one direction.

A small resistor R2! may be placed in series with the motor to hold the current therethrough to a, safe value in case oi jamming of the throttle mechanism or other misoperation. Switches S2 and S3, which in practice may be one double pole switch mounted on the pitch control stick 5, can be used for disconnecting the motor. .Another resistor R22 is connected across the motor 4 and the switches S2 and S3.

The power supply for the control unit may be a 24 to 28 volt battery. The tubes Vi and V2 may be the two halves of a type J tube. Tubes V3 and V4 may each be a type iZATB tube. Tubes V5 and V6 may also'be 2 sections of a @Je tube. Tubes Vl and V8 may be the two sections ci a type ZSD'H tube. The battery supplies the necessary heater currents and a B+ voltage of about l2li volts. By means of a regulator tube V9, which :may be an Amperite 4RM tube, a regulated B+ voltage of about 12 volts is obtained and applied to the potentiometers Pd and P5.

In normal operation of my apparatus only the potentiometer P3 is varied to vary the engine speed. The range of engine speeds available is determined by the setting of potentiometer Pi. Since thisl range is fairly wide the main effect of varying potentiometer Pi is to limit the maximum engine speed. When the engine is running at its proper speed the voltages derived from the rectiers balance each other. if the proper speed is exceeded the voltage across the high pass ilter increases and a voltage is impressed across ren sistors R5 and Rl. Ii the engine speed should decrease below the proper value the voltage across the resistors R5 and Rl will change its polarity. The magnitude of this voltage will be determined by the magnitude or the deviation from the proper-speed. iThis voltage causes the acceleration or deceleration multivibrator to oscillate, and thereby determines the direction oi rotation of the motor 4, which in turn determines whether the engine will be accelerated or decelerated. The multivibrators oscillate as long as a suilicient positive voltage is applied to the grid of the rst tube, V3 or V0. The rate of oscillation, or the repetition rate, depends on the magnitude of this grid/voltage. Consequently the rate of correotion depends on the magnitude of the speed den viation. The deviation required to initiate a correction is adjusted by the tolerance control potentiometers Pl. and P5.

For the purpose of explaining the invention a specific embodiment thereof has been described in detail, but it will be apparent to those skilled in the art that many changes other'than those mentioned can be made without departing from the invention. `and the latter is. thereforen to be limited only to the extent set forth in the appended claims.

I claim:

1. Apparatus for controlling the speed of an engine comprising a winding operated through rotation of the engine to produce an alternating voltage signal, means for converting a rst portion of said signal into an intelligence signal which varies in 'accordance with the speed of said engine, means for converting a second portion of said signal, into a reference signal which, compared to theintelligence signal, is relatively invariant with the speed of the engine, a pair of multivibrators respectively /responsive to said intelligence and reference signals for generating pulses having a repetition rate corresponding to the magnitude, respectively, of the said intelligence and reference signals, a reversible motor controlled by said multivibratnrs and a high pass filter i'n the circuit of said intelligence signal, said illter having a voltage output of increased magnitude with the increase of speed of said engine, and a low pass nlter in the reference signal circuit for maintaining said reference signal of a substantially constant magnitude.

2. Apparatus for controlling the speed of an engine comprising a winding operated through rotation of the engine to produce an alternating voltage signal of a frequency corresponding to the speed of the engine, means for converting a ilrst portion oi' s aid alternating voltage signal to a direct current intelligence voltage varying in magnitude in accordance with the frequency thereof, means for converting a second portion of said alternating voltage signal into a reference voltage of a magnitude which is substantially invariant with respect to the speed of the engine, means for combining said intelligence and reference voltages to obtain a third voltage whose polarity and magnitude correspond to the sense and magnitude, respectively, of the output of the winding, ilrst and second multivibrators for producing pulses of varying widths and repetition rates, said third voltage being operative to alternatively trigger each of said multivibrators when the speed of the engine deviates from a predetermined speed and so as to determine the pulse width and repetition rate of `each multivibrator. and a servo motor connected to said multivibrators so as to receive direct current pulses of one polarity from one of said multivibrators and of the other polarity from the other of said multivvibators.

JOHN J. ROOT.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Curtis Jan. 25, 1949 

